In recent years, demand for specifications of products from customers has been diversified. In order to satisfy this diversified demand, there have been increased cases where specifications of products are differentiated for respective destinations of the products. In addition, in order to satisfy users' desires, new models have been added and the number of types of products has been increasingly grown.
Therefore, it is necessary to manufacture various types of models in a small amount (perform high-mix low-volume production) without reducing a rate of operation, by altering typical equipment that has performed low-mix high-volume production.
There are various tasks to mixedly manufacture various types of products in a typical equipment (line). The most conspicuous task is to correctly determine a plurality of types of workpieces moving down the line (e.g., assembly line) to thereby unmistakably execute assembly work or processing work different for each type of product.
For example, there is a conveyance line of cylinder blocks, which are castings or the like, in a manufacturing facility of engines for automobiles. A plurality of types of cylinder blocks serving as workpieces mixedly moves on this conveyance line in many cases. Therefore, it is necessary to identify types of cylinder blocks and sort the cylinder blocks according to the types at an entrance or exit of the conveyance line. In addition, it is known that the following identification methods are generally used, instead of a contact-type displacement sensor. Specifically, a barcode, which is a protruding portion, is formed on a casting or the like moving down the conveyance line. This barcode is obliquely irradiated with light from a light emitting source, and therefore a shadow of this barcode is formed. Then, an image of this shadow is captured by a TV camera and predetermined information processing is performed, and therefore, the type of the casting or the like is identified.
Further, the following detection method is also carried out. A barcode, which is a protruding portion, is integrally casted with a reference bar on a circumference surface of a cylinder block that is a casting serving as a target to be identified. A model number, a mold number, and the like are expressed by the number of protruding portions and intervals therebetween. The model number, the mold number, and the like are detected by a TV camera.
Further, as disclosed in, for example, Patent Literature 1, the following technology is also known. In order to reduce the number of integrally casted protruding portions, in other words, reference bars, a casting or the like is identified by obtaining widths and heights of the bars. A plurality of types of castings or the like is identified by changing the heights or the widths of the bars for each type of casting or the like.
Further, as disclosed in, for example, Patent Literature 2, the following technology is also known. In order to correctly identify various types of workpieces fed into a conveyor, a distance from a surface of a workpiece and presence/absence of a blind bore on the surface of the workpiece and a position thereof are obtained by a displacement laser sensor serving as an optical measurement device.
Further, as disclosed in, for example, Patent Literature 3, the following technology is also known. By optically examining an external form without contact, instead of using a contact-type displacement sensor, highly accurate detection is carried out without receiving a harmful influence such as a positional shift of a workpiece.
Further, as disclosed in, for example, Patent Literature 4, the following technology is also known. In an ultrasonic sensor, a reflection amount or transmission amount of ultrasonic waves is different depending on a material of an object. In order to avoid false detection caused by this fact and achieve stable detection, a distance calculation unit calculates a distance from an object on the basis of time between a timing at which ultrasonic waves are emitted and a timing at which reflected waves are detected. The type of the object is detected on the basis of the calculated distance and a receiving amount received by an ultrasonic wave transmission and reception unit.
Further, as disclosed in, for example, Patent Literature 5, the following technology is also known. A photoreflector is used as a release switch of a camera in order to achieve releasing of a camera without contact and reduce an influence of camera shake caused by release operation.